boysnew socks NEXT 9-12? or 12.5-3.5 £3.50

BOYS NEXT 5 pack socks new with tags
they are black with a bright coloured tip
i bought these for my son thinking he would grow into them but they are even huge for my nephew
they are labelled 9-12 but this is wrong as they are bigger and must be the next size up which is 12.5-3.5
thanks